Conventional musical drums with one playing means are often cylindrical with the playing means, typically a drumhead, on the top surface of the drum and an open air portal on the bottom surface of the drum.
In conventional drums with two playing means, one playing means is on the top surface of the drum, a second playing means is on the bottom surface of the drum and a small air portal is disposed on the cylindrical surface of the drum.
Attempts to vary the pitch of these drums while they are being played generally has involved the use of means to vary the tension on one of the playing means or heads of the drum. A more conventional way of providing drums with different pitch has been the use of drum sets in which each drum of the set is of a different size or the heads have different tensions applied to them. Caribbean steel drums are constructed such that each of several areas of the surface yields a different tone when struck. However, in the Caribbean steel drum, the pitch obtained by striking a given area cannot be varied.
In most conventional drums the air portals function passively and are not played by the percussionist. Hence, in those conventional drums the air portals are not playing means. There are drums, such as the ghatam from India, in which the player can vary the pitch by partially occluding an air portal while striking a rigid drum shell.
Prior to playing a drum, percussionist often stretch or loosen the drum heads to tune the drum to a desired pitch. Sapp, in U.S. Pat. No. 635,192, introduced an expansile head-tensioning tube to uniformly stretch a drum head around its circumference. Although the means employed by Sapp permits one to variably tune a drum prior to playing the drum, Sapp's invention does not permit the pitch to be varied as the drum is being played.
This invention introduces means of changing the pitch of a drum, while the drumhead is being played, by varying the volume of air inside the drum, by varying the rate of air flow into or out of the drum or by a combination of these two principles. Additional variation in pitch is obtained by providing multiple playing means on an individual drum.